The object of the present invention is a stretcher for tubular knitwear fabric, especially for application to calenders or other machines for the treatment of tubular fabric.
It is known that stretchers are used during the finishing step of tubular knitwear articles for stretching and spreading the tubular article in order to ease the finishing operations.
Thus in calendering, which is usually the last finishing operation, it is necessary to use a stretcher in order to achieve a uniform vaporisation and to adjust the width of the tubular article to the desired value.
Stretchers are known, such as, for example, the one protected by the european patent No. 0791092 assigned by the same Applicant of the present invention, in which the fabric is pressed between a ring or a shaped wheel and two inclined wheels, and consequently streaks or marks can be produced into the fabric. In this patent, the above embodiment is for keeping the stretcher arms in the right position by means of the pressure said inclined wheels exert against the shaped wheel, with the consequence of a pressure onto the fabric and thus of possibly damaging it.
Another stretcher of the prior art is protected by french patent No. 2.592.897, in which the vertical stretcher arms, besides being attracted outwards by a magnet so that they are kept in the right position, are also pushed by means of parallelograms that can be deformed by pressure, said parallelograms being interposed between the arms against the fabric advancing wheels.
This embodiment has the draw-back that said deformable parallelograms not only provide safety in case the magnets should not work properly, but also exert an excessive pressure onto the fabric against the driving wheels, thereby producing marks or streaks onto the fabric. This pressure is always acting, also when the sole attraction force of the magnet would be enough.
The purpose of the present invention is to obviate these draw-backs, with the advantage that between the stretcher arms there is no pressure member. Only the inclined wheels, which are constantly offset from the shaped wheels that are applied to said arms, because they are attracted by the magnets, might, in an emergency case, press the fabric against the shaped wheel, but only for a short time because upon adjustment of the magnet the inclined wheels are immediately removed from the shaped wheel that goes into contact with the driving wheel.